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TPS780: Most common design failures

Daniel Martinez
Prodigy 10 points
Part Number: TPS780

Tool/software:

Good afternoon,

We are currently experiencing a strange behaviour on a TPS78001. The output of the chip is programmed to work at 3.2V, using a voltage divider in the output of R1=715k, R2=442k with a 10p cap in parallel to R2. Vin=5V. 

When the sensor is defective, the Vout is 3V (stable) instead of 3.2V, and after a random period of time (from seconds to minutes, to days), the Vout drops to 2V (roughly). The failure is the same in all the sensors already analyzed. The chip is embeded in Epoxy. 

My questions are the following:
- Which are the most common causes of failure on the chip and why are they caused. 

- Based on your expertise, have you even seen a similar error? 

- Looking at the forum, I saw that other user had back flow current problem, and the Ouput Voltage was 3.7V stable, rather than 3.3V. Is it a common behaviour that the voltage is "constant" after a failure? Why is this happening?

  • 0
    TI__Mastermind 37065 points

    Hi Daniel,

    I've looked through our internal archives and I don't see anything like this issue for this LDO.  The archives are simply test measurements that customers have requested.  I don't see failures associated with this device.  This is an older device and the lack of this data suggests that this is a robust LDO. 

    If your output voltage is powering a defective sensor, and the output voltage droops over time, then that sounds like excessive loading on the LDO causing it to droop.  The LDO may be in current limit.  Can you provide a schematic?  Can you provide oscilloscope plots showing Vin, Ven, Vout and Iout?

    Thanks,

    Stephen